Detonation pick-up and igniter unit



e ESL Feb. 13, 1962 FIG .1

INVENTOR V/NCENT C. DA V/S ATTORNEYS United States Patent 3,020,763 DETONATIDN PICK-UP AND IGNHTER UNIT Vincent C. Davis, Richmond, Calif., assignor to California Research Corporation, San Francisco, Calif., a corporation of Delaware Filed Nov. 7, 1958, Ser. No. 772,596 1 Claim. (Cl. 73-389) This invention relates to improvements in piezoelectric pressure indicators, such as are used to detect detonation in the cylinders of internal combustion engines, and particularly refers to a unitary structure which combines the functions of a pressure pick-up and an igniter or spark plug by appropriate and novel modification of a commercial spark plug unit, to be described below.

Heretofore, units of this type have been characterized by excessive complexity and consequent high cost, as well as large size and a multiplicity of delicate parts which were susceptible to changes in response characteristics during extended operation. This unit may be briefiy characterized by the utilization of certain of the normal components of a conventional spark plug, viz, the outer threaded shell and the refractory insulating core and its axial electrode. To place a piezo-element in position to respond to pressure changes in the internal combustion engine cylinder, it has been found necessary to provide a resilient seal between the usual enlarged portion of the core and the surrounding shell. Desirably, an electrically conductive coating is fired onto the ceramic core to act as part of the electrical circuit of the unit and also to shield electrostatically the piezo-element, and render more usable the signal it generates.

Above the enlarged portion of the core there is provided an annular follower element to transmit thrust to one or more annular piezo-elements, the uppermost face of which is restrained by an overlapping tension member threaded securely into the metal shell of the unit. Suitable electrical insulation and leads are provided to conduct out of the unit the electrical response of the piezoelement or elements due to the mechanical force changes imparted to it by the rapid pressure changes in the engine combustion chamber. The high voltage supply to the igniter electrode is unchanged.

It is an object of this invention to provide a compact and simple unit combining the functions of the usual spark plug and means incorporated entirely within the body of it responsive to rapidly varying pressure changes in the engine cylinder.

Another object is to provide a novel structure that utilizes certain of the parts found in a conventional spark plug, but with modifications and additions that render them usable in their new relationship.

These and other objects and advantages will be further apparent from the attached drawing and the follow ing specification which illustrates and describes a preferred embodiment of the invention.

In the drawing, FIGURE 1 is an enlarged side elevational view, partly in longitudinal section, of a spark plug modified to embody the invention.

FIGURE 2 is a detailed and still further enlarged vertical sectional view of an alternative arrangement of a single piezo-element and its associated tension and folwith its lower end spaced a few thousandths of an inch from an appropriate transverse metal ground electrode or tip 15 secured to the bottom of shell 10 and adapted to project into the combustion chamber. An appropriate source of ignition voltage, comprising the usual distributor and associated electrical system (not shown) is connected to the metal cap 16 at the top of core 13 to fire the ex plosive charge in the engine cylinder.

Intermediate the ends of core 13 is the usual enlarged diameter portion 17, having an upper face 18 and a lower face 19, as shown. Desirably, that portion of core 13 between the lower smaller diameter portion below face 19 and the upper serrated. portion 20 near the top of the core is coated with an electrically conducting layer, such as a thin vitrified coating of platinum or other appropriate metal 21, as indicated by the stippled area of FIGURE 1, for purposes to be described below.

To seal the core 13 to the bore of shell 1%, a thin flexible metal annular diaphragm 22 is placed below face 19 and silver-soldered at 23 and 24 to the metal of shell 10 and a suitably fiuxed portion of the core, respectively. Well known metal-ceramic bonding materials may be used for this purpose. Core 13 is thus resiliently supported in shell 10 so that pressure changes in the combustion chamber are transmitted to the bottom of the core 13 and diaphragm 22.

Surrounding core 13 above the enlarged diameter portion 17 is an annular metal sleeve or follower member 25 having a lower rounded end to engage the upper face 18 of the core, and a fiat upper face on which rests a thin annular metal electrode 26. On top of electrode 26, in the arrangement of FIGURE 1, are two annular piezoelements 27 and 28, separated by a fiat annular metal electrode 29, the latter having a small radial projection or tip 30 to which an insulated electrical conductor or lead wire 31 may be soldered.

Above the uppermost piezo-element 28 is another annular electrode 32. The two outermost electrodes 26 and 32 are primarily designed to make a good electrical and mechanical contact with the plane faces of piezo-elements 27 and 28, and could equally well comprise a thin electrolytically deposited metal coating on the element itself, or could be omitted entirely, if the top faceof follower member 25 and the shoulder 33 of the tension member 34 are sufficiently plane and parallel.

Tension member 34, in this example, comprises a sleeve having the inwardly projecting shoulder 33 near its upper end, and an externally threaded portion 35 at its lower end to be received in corresponding internal threads at the upper end of shell 10. At a convenient point in its upper end, member 34 is provided with a threaded bore 36 to receive a conventional connector generally designated 37 for conductor 31, which conveys the electrical response of piezo-elements 27 and 28 to suitable electrical indicating means. As these last-named means form no part of the present invention, they are not shown herein.

Alternatively to this arrangement of the opposed piezoelements 27 and 28 with an intermediate electrode 29,

there may be used a single piezo-element 38 as shown inv the enlarged fragmentary detail view of FIGURE-2. In that figure, the upper electrode 292 is connected to the lead conductor 31 at the point where bore 36 intersects the bore of tension member 34, as will be apparent to one skilled in this art. To insulate electrode 292 from the tension member 34, a suitable insulating washer 39 of mica or the like is provided as shown.

In operation, the assembled unit is screwed into the usual threaded opening in the engine cylinder, and the cap 16 is connected to the engine ignition system. Conductor 31 and the grounded shell 10 of the unit are connected to the conventional metering device for indicating the voltage changes due to forces exerted on piezo-elements 27, 28 or 38 by pressure changes in the engine cylinder. These changes are exerted against the lower end of core 13 and resilient diaphragm 22 and are transmitted as mechanical forces by upper shoulder or face 18 of the core to the follower member 25 and ultimately to the piezo-element or elements, the upper faces of which are restrained by tension member 34.

Desirably, but not necessarily, a heat-conveying means is provided to transmit heat from core 13 to shell and thereby to limit the temperature rise of the piezoelements. In this example, it comprises a quantity of discrete granules 40 of a suitable metal, e.g., silver, supported on diaphragm 22 and retained in position as by an O-ring 41 of heat-resistant plastic.

It has been found that the piezo-elements, which may be quartz crystals or ceramiomixtures, are adequately electrostatically shielded by their position between the electrically conductive coating 21 on core 13, which also serves to complete the electrical ciruit between follower and shell 10 by way of diaphragm 22 and the metal tension member 34. If the coating 21 should be omitted for any reason, an auxiliary connector such as a flexible metal spring could be arranged between follower 25 and the bore of shell 10 to complete the electrical circuit.

In conclusion, it will be noted that there has been provided an improved pressure pick-up and igniter unit for the purpose described, characterized by a flexible annular support connecting the core to its enclosing shell, with one or more piezo-elements retained between the core enlargement and an overlying tension member to be responsive to rapid changes in engine cylinder pressure. Although only a single exemplary embodiment has been illustrated and described, it is apparent that numerous changes could be made without departing from the essential features of the invention, and all such modifications that come within the scope of the appended claim are intended to be embraced thereby.

I claim:

A combined spark plug and engine pressure pick-up in the form of a normal spark plug comprising a refractory insulating core of generally cylindrical form having an electrode extending axially therethrough, a radially projecting portion formed integrally with said core and positioned adjacent to and in spaced-apart relationship from the lower end thereof and defining radially extending circumferential upper and lower shoulders, a thin layer of electrically conducting material deposited on the exterior surface of said core throughout the middle egion thereof and excluded from the end regions of said core, a hollow metallic shell of generally cylindrical form surrounding the lower portion of said core in radially spaced-apart relationship thereto, an annular diaphragm surrounding said core below and adjacent to said lower shoulder and extending radially to the inner wall of said shell and secured in fluid-tight relationship to said core and to said shell, a quantity of metal granules supported on the upper surface of said diaphragm and filling the space between said core and the inner wall of said shell in the region of said radially projecting portion of said core, a packing means circumferentially surrounding said core adjacent said upper shoulder and contacting said projecting portion of said core and the said inner wall of said shell and retaining said metal granules in position, a hollow cylindrical element surrounding said core in the middle region thereof in slidable relationship and seated at its lower end on said upper shoulder and constructed to apply pressure to said packing means, a radially outwardly extending circumferential shoulder formed on the upper end of said cylindrical element, at least one annular piezoelectric element supported on said shoulder of said cylindrical element, an annular tension member threaded into said upper portion of said shell and extending axially upward therefrom and having a radially inwardly projecting circumferential shoulder formed integrally therewith and positioned to engage the upper surface of said piezoelectric element and compressing said piezoelectric element against said shoulder on said upper end of said cylindrical element and compressing said lower end of said cylindrical element against said upper shoulder of said radially projecting portion of said core, an electrical conductor operatively attached to said piezoelectric element, an electrical connector secured to said tension member and having a passageway therethrough through which said electrical conductor is passed.

References Cited in the file of this patent UNITED STATES PATENTS 2,068,744 Gutzke Jan. 26, 1937 2,190,713 Hintze et al Feb. 20, 1940 2,460,022 McCarthy et al Ian. 25, 1949 2,738,677 Li Mar. 20, 1956 2,902,747 Reiter Sept. 8, 1959 

